DYNAMICS OF THE DEVELOPMENT SALT-DOME STRUCTURES OF THE CENTRAL PART OF THE DNIEPER-DONETS DEPRESSION

Abstract

The Dniprо-Donets Depression is the main oil and gas region of Ukraine. The region is characterized by a wide distribution of salt dome structures that are objects of oil and gas exploration. The complex and long history of the region’s formation caused the creation of the structural-tectonic zonation of the Dniprо-Donets Depression, which includes: the northern and southern marginal (near-edge) zones (or seam zones of the Pripyatsky-Manitsky and Baranovitsko- Astrakhansky deep faults), pre-axial (or zones of near-ridge basement protrusions) and axial zones. The southern and northern marginal (edge) zones are the immersed slopes of the Ukrainian Shield and the Voronezh Crystalline Massif. Riftogenesis and halokinesis were the factors that have influenced the cyclical course of the evolution of salt domes, for which the asynchronous level of development was characteristic in certain geological epochs, due to their confinement to different structural and tectonic zones of the depression. The morphological features of salt structures, the distribution and nature of disjunctive dislocations, stratigraphic and lithological gaps and unconformities are reflected in the distribution of oil and gas traps. In developed oil and gas regions, where tasks of geological exploration works become more complicated, the value of paleotectonic researches for forecasting traps and their oil and gas content is substantially increased. The main stages of the formation of salt structures located in the axial, southern and northern marginal structural and tectonic zones of the depression on the graphs of sedimentation rates are considered. When comparing charts of sedimentation rates according to the wells data, in the Tournaisian through the early Permian interval there is a synchronous (according to the epochs) jump-like character of the development of structures, regardless of their location within structural and tectonic zones is observed. The general slowdown of sedimentation rates from the Paleozoic to the Mesozoic, from the Mesozoic to the Cenozoic era, is characteristic for the whole territory of the Dnipro-Donets Depression. For the Kreminkivskaya-402 borehole maximum values correspond to the Middle and Late Devonian and Bashkirian, middle values to the Late Visean, Serpukhovian, and the minimal values – to the Tournaisian and Early Visean time. For the Skorobagatkivska-2 borehole the maximum values correspond to the Middle and Late Devonian, Late Visean, Bashkirian and Late Carboniferous, the middle values correspond to the Tournaisian- Early Visean and Moscovian, and the minimal values – to the Serpukhovian and Early Permian. For the Herasymivska-1 borehole the maximum values are characteristic for the Middle and Late Devonian, Late Visean and Bashkirian; the middle values – to the Tournaisian and Moscovian, and the minimal values – for the Late Visean and Serpukhovian.